Effects of nested plot designs on assessing stand attributes, species diversity, and spatial forest structures

Abstract

Nested plot designs are widely applied because they increase efficiency in estimating total volume by using smaller nested subplots to reduce effort in measuring small trees. However, they may not be optimal for characterizing other forest structures. The objectives of this study were to assess the performances of nested plot designs in estimating stand parameters, and local-level species diversity and spatial forest structures through simulation. Three 25–50 ha census plots in tropical and subtropical forests were used. Ten nested plot designs with varying number of nested subplots and diameter at breast height (dbh) thresholds were simulated. Baseline comparison was a circular plot in which all trees were assessed. Results indicated that number of trees per hectare and basal area per hectare were unbiasedly estimated. However, all nested plot designs underestimated species richness and species mingling. Three variations of Clark & Evans Aggregation Index describing spatial forest structures were generally overestimated by the nested plots. Generally, nested plots were less efficient in estimating the forest structures compared to the baseline. This study has demonstrated that nested plot designs may not adequately capture multiple aspects of forest structures, and the need to balance accuracy, efficiency, and field effort.